Droplet separator

ABSTRACT

A droplet separator for removing liquid droplets from a gas stream entraining same, comprises a stack of corrugated plates having a given crest-to-crest spacing which can be represented as a wavelength λ and collecting pockets at each crest having inlet slots opening into the oncoming gas stream. Each plate consists of a plurality of plate members whose length, measured parallel to the wavelength measurement, is greater by the distance of the overlap of these plate members at each crest than n λ/2 where n is 1/2 or 1.

CROSS REFERENCE TO RELATED APPLICATION

The present application is related to my application (disclosing anearlier version of the present device) Ser. No. 665,869 filed Mar. 11,1976, now abandoned, which, in turn, refers to U.S. Pat. No. 3,849,095.

FIELD OF THE INVENTION

The present invention relates to a device for the removal of liquiddroplets from a gas stream entraining same and, more particularly, to aliquid droplet separator of the type which induces change in directionof a gas stream through flow passages defined between corrugated platesprovided with liquid-collecting pockets at the crests of these plates.

BACKGROUND OF THE INVENTION

In the aforementioned copending application and in my earlier work asdescribed above and including German Auslegeschrift DT-AS 22 51 173(U.S.Pat. No. 3,977,977), there have been described droplets separators ofthe aforedescribed type operating on the principle that repeateddirection change of a gas stream subdivided into individual streamletsbetween plates of a stack will cause the release of the droplets byinertia. In other words, the momentum or inertia of the liquid dropletscauses them to be carried against the walls of the plates and into theliquid-collecting pockets at the crests of the corrugated plates, thesepockets forming vertically extending ducts by which the liquid isdischarged. The gas traversing the stack of plates is thus substantiallyfree from droplets above a given particle size.

Notwithstanding the aforementioned teachings, and previous work in thisfield, the relationships between the plate characteristics, theflow-passage length and the interplate spacing have not been fullyunderstood vis-a-vis an optimum removal of liquid droplets from a gasstream. Considerable effort has, therefore, been expanded in perfectingsuch particle droplet separators.

OBJECTS OF THE INVENTION

It is an object of the invention to improve the particle dropletseparator described in the prior application and in the publicationsmentioned therein and hereinabove so as to obtain optimum liquid-dropletremoval from a gas stream.

A corollary to this object is the object of eliminating certaindisadvantages of the earlier system, whether these disadvantages derivefrom designed considerations, are problems of low efficiency, or aredifficulties encountered with removing droplets up to a limiting minimumparticle size.

SUMMARY OF THE INVENTION

These objects and others which will become apparent hereinafter areattained, in accordance with the present invention, in a dropletseparator for removing liquid droplets above a minimum limiting dropletdiameter d from a gas stream entraining the droplets with a defineddroplet-size spectrum at an inlet velocity v. The droplet separatorcomprises a stack of vertically extending corrugated separator plateshaving an interplate spacing T, a crest-to-crest spacing along eachplate of the value λ, and collecting pockets at each crest having inletslots opening into the oncoming gas stream traversing respective flowpassages between each pair of plates from an inlet side of the stack toan outlet side thereof. These passages have a length measured in astraight-line dimension between the inlet and the outlet sides of thevalue L_(K).

Hereinafter, the aforementioned crest-to-crest spacing λ is alsoreferred to as the "wavelength" by analogy to sinusoidal waves. In fact,the corrugated plates are preferably sinusoidally corrugated.

According to the invention, each of the plates is formed by a pluralityof plate members of a length L_(T) measured along the aforementionedstraight-line dimension, the successive plate members of each plateoverlapping over a distance U along the straight-line dimension at arespective pocket.

It is also essential to the present invention that the length L_(T) isgreater by the distance U than the value nλ/2 where n is 1/2 or 1.

According to another essential aspect of the invention, the passagelength L_(K) is substantially equal to mλ/2 where m is an integer.

Also essential to the invention is the fact that the product of theinlet velocity v and λ, i.e. vλ, corresponds to the product of thepassage length L_(K) and a characteristic velocity v_(c) constitutingthe allowable inlet velocity of the droplet separator at which thespacing T defines the limiting droplet diameter.

To clarify the significance of the fact that the length L_(T) is greaterby the distance U than nλ/2 where n is 1/2 or 1, it can be observedthat, where the overall length of the flow passage L_(K) is equal toλ/2, i.e. m = 1, the partial plates or the plate members constitutingeach of the corrugated plates, will have a length measured parallel tothe dimension L_(K) which is equal to λ/4 + U. In this case, of course,n = 1/2. Normally, however, the passage length will be equal to λ ormore in which case n = 1.

The permissible inlet velocity of the droplet separator for a flowpassage length L_(K) = λ is defined as that inlet velocity at which apredetermined limiting droplet diameter d exists above which diameter,all droplets are removed.

It has been found, most surprisingly, that when the plate spacingcorresponding to the dimension T has a given value T1 corresponding to alimiting droplet diameter d_(T1) it is possible to determine the spacingT2 for any other limiting droplet diameter d_(T2) from the relationship(d_(T1) /d_(T2))² = T1/T2. Obviously, this relationship also determinesthe ratio of the limiting droplet diameters which can be obtained for agiven ratio of interplate spacings under the conditions set forth above.

I have found, according to another feature of the invention, that thespacing T should range from 15 to 30 mm practically in all cases inwhich industrial exhaust gases are to be stripped of liquid droplets.When this interplate spacing is used, the wavelength λ should be between2 and 7 times the interplate spacing T.

According to still another feature of the invention, the plate members(partial plates of each of the separator plates) abut one another at theedges of the slots of the respective pockets turned toward the oncominggas stream, via gap-defining elements which may be deformed in the platemembers or disposed between them as separate members.

According to still another feature of the invention, which has beenfound to increase still further the degree of separation in the finedroplet region of the droplet-particle spectrum, the discharge or outletportion of the stack is formed with mutually parallel walls generallylying in the flow direction but formed with undulations, e.g. ofsinusoidal configuration, whose wavelength (crest-to-crest spacing) issmall in proportion to the wavelength λ of the corrugated plates formingthe main portion of the stack.

The advantages attained with the present system include increasedseparating efficiency and the ability to establish without trial anderror the parameters of a particle separator which will ensure removalof liquid droplets above limiting particle diameters which can vary fromcase to case and for different inlet flow velocities which may likewisevary from one application to another of the droplet separator.

The apparatus of the present invention can thus be used for differentgases with different separating effects, as required, and the apparatuscan be assembled from standarized units to provide flow passages ofdiscrete lengths, i.e. λ/2, λ, 3λ/2, 2λ, 5λ/2 . . . , with optimizationof the effect simply by choice of the desired flow passage length.

Furthermore, the present arrangement of plural plate members toconstitute each of the plates permits the overlap of the plate membersto be adjusted, the depth of the collecting pockets to be variedindependently of the pocket overlap and the number of pockets to beestablished with relatively simple means, e.g. the insertion of spacersbetween the plate members, for optimization of the particular separationwhich is to be undertaken.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of the presentinvention will become more readily apparent from the followingdescription, reference being made to the accompanying drawing in which:

FIG. 1a is a horiztonal cross section through a portion of a plate stackof a droplet separator embodying the invention;

FIG. 1b is a similar view of another embodiment of the invention;

FIGS. 1c and 1d are further illustrations similar to FIGS. 1a and 1b ofother embodiments of the invention, it being noted that the partialFIGS. 1a through 1d illustrate different arrangements of the plates ofthe stack corresponding to different inlet flow velocities for a givenlimiting droplet diameter d;

FIG. 2 is a view similar to that of FIGS. 1a through 1d, althoughgreatly enlarged in scale, illustrating still another droplet separatorand showing details of the construction thereof;

FIG. 3 is a section, further enlarged in scale through the particleseparator of FIG. 2 in the region III thereof;

FIG. 4 is a view similar to FIG. 2 illustrating another embodiment; and

FIG. 5 is a detail view of the region V of FIG. 4.

SPECIFIC DESCRIPTION AND EXAMPLE

The device illustrated in the drawing is a droplet separator for theremoval of liquid droplets from a flowing gas stream. The gas flowdirection has been represented by the single headed arrow v in thedrawing, the arrow v representing in each of the embodiments of FIGS. 1athrough 1d a vector illustrating the inlet velocity and magnitude. Thegas stream entrains droplets of a defined droplet size spectrum and thedevice is constructed to remove droplets of a diameter above the dropletlimiting diameter d substantially completely, i.e. the gas streamemerging from the unit should be free from droplets of a diameter largerthan d.

The apparatus comprises, in addition to the usual housing (not shown)and means for forcing the gas stream therethrough a stack of preferablysinusoidally corrugated plates 1 which are disposed vertically and haveat their crests 2 collecting pockets 3 which open at slots 3a generallyinto the direction from which the stream arrives, i.e. into the oncominggas stream. As has been illustrated in FIGS. 2 and 4, the stack may alsocomprise parallel-wall inlet sections 4 and parallel-wall outlet section5.

As can be seen from the embodiments of FIGS. 1a through 1d, each pair ofplates 1 defines between them a flow passage 6. It is customary tosupply a multiplicity of such passages and in the embodiments of FIGS.1a through 1d, 2 and 4, it will be understood that the single passage ortwo passages illustrated are only representative of a multiplicity ofsuch passages and the corresponding number of parallel corrugated plates1.

The corrugations of the plates 1 define a wavelength λ which can beconsidered as the intercrest or crest-to-crest spacing. The value λ hasbeen shown in FIG. 1b by a corresponding double-headed arrow.

In each of the Figures, where convenient, a double-headed arrow L_(K)represents the flow-passage length as measured parallel to the inletvelocity vector v.

The plates are generally so oriented that the collecting passage 7formed by each pocket 3 lies substantially vertically, i.e.perpendicular to the plane of the paper in FIGS. 1 through 5.

As a comparison of the Figures will show, each of the corrugated plates1 is composed of substantially Z-shaped or S-shaped plate members a andb which overlap at regions 8 defining the pockets 3. The overlapdimension has been shown by the double-headed arrow U in the drawing.

According to the invention, the partial-plate length L_(T), i.e. thelength parallel to the inlet vector v of one of the plate members a, bdefining each plate 1 is greater by the pocket overlap dimensions U thanthe half wavelength λ/2. This corresponds to a value n (as definedpreviously) equals 1.

The plates 1 of each stack can be assembled from a succession of theplate members a and b as a comparison of FIGS. 1a through 1d will showso that the flow passage length L_(K) corresponds to an integral numberof half wavelengths λ/2, i.e. m = an integer. In addition, the productof the inlet velocity v and the wavelength λ is as close as possible tothe product of the flow passage length L_(K) and a characteristicvelocity v_(c).

This characteristic velocity of the gas is defined as the permissible orallowable inlet velocity of the device for the flow passage length L_(K)= λ for an unchanging (constant) particle size distribution dropletspectrum and interplate spacing.

The interplate spacing T thus defines the limiting droplet diameter d.

At the left hand side of each FIGS. 1a through 1d, the velocity vector vhas been shown while the flow passage length L_(K) in terms of λ hasbeen shown on the right hand side of each FIGURE. It is thus readilyapparent that, for a given interplate spacing T and particle sizedistribution, the same limiting particle diameter d will pertain toincreasing velocities v with corresponding increases in the flow passagelengths by units of λ/2.

If it is desired to change the limiting droplet diameter d, theinterplate spacing T is varied. It has been found that once the spacingT1 is ascertained for a given droplet diameter d_(T1), all otherconditions being the same, the spacing T2 for any other particle sizelimiting diameter d_(T2), is given by the relationship (d_(T1) /d_(T2))²= T1/T2.

It will be also apparent from this relationship and the drawing that, ifthe limiting particle size diameter d is to be greater by the factor 2,the spacing T must be increased by the factor 4. In industrial practice,the spacing T should range between 15 and 30 mm for the processing ofindustrial waste gases. The wavelength L, by way of specific example ofthe best mode or practicing the invention, should be between 2 times and7 times the interplate spacing T.

The embodiment of FIG. 2 shows that the pockets 3 may be provided withgap-defining elements 9 as constituted as formations deformed directlyin the plate members. This can apply also for the plate members of FIGS.1a through 1d.

Formations 9 are protuberances formed on one of the plate members andengaging the other plate member defining the respective pocket at thedownstream side thereof.

In FIG. 4, I have shown an arrangement whereby pocket-forming elements10 are provided, these elements being integral with the plate membersand bent from parts thereof or being constituted as separate piecesattached thereto. The outlet portion 5 of the stack has the parallelwalls formed by the plates 1 provided with corrugations 11 whosewavelength is relatively small in comparison to the wavelength λ of theplates 1. The pockets of the embodiment of FIG. 4 can have a variablevolume as a result of relative shifting of the plate members of eachplate as illustrated in broken lines in FIGS. 2 and 4. In FIG. 5, themembers forming each pocket are shown to have spacing elements 12disposed therebetween to permit variation of the pocket volume. Thespacer elements 12 can be welded in place and can be corrugated stripsextending in spaced apart horizontal planes.

I claim:
 1. In a droplet separator for removing all liquid droplets of asize above a minimum limiting droplet diameter d from a gas streamentraining said droplets with a defined droplet-size spectrum at aninlet velocity v and comprising a stack of vertically extendingcorrugated separator plates having an interplate spacing T, acrest-to-crest spacing λ on each plate and collecting pockets at eachcrest having inlet slots opening into the gas stream traversingrespective flow passages between said plates between an inlet side ofsaid stack and an outlet side thereof, said passages having a lengthL_(K) measured in a straight-line dimension between said inlet andoutlet sides, the improvement which comprises, in combination with meansfor supplying the gas stream to said inlet side of said stack at saidvelocity v:(a) each of said plates is formed by a plurality of platemembers of length L_(T) measured in a straight-line dimension betweenthe inlet and outlet sides of the stack, the successive plate members ofeach plate overlapping over a distance U measured in a straight-linedimension between the inlet and outlet sides of the stack at arespective pocket; (b) the length L_(T) being greater by the distance Uthan nλ/2 where n is the number selected from one half and one; (c) saidpassage length L_(K) is substantially equal to m λ/2 where m is aninteger; and (d) the product of the inlet velocity v and λ correspondsto the product of the passage length L_(K) and a characteristic velocityv_(c) constituting the allowable inlet velocity of the separator atwhich the spacing T defines the limiting droplet diameter d, λ beingbetween 2 and 7 times T.
 2. The device defined in claim 1 wherein for agiven interplate spacing T1 corresponding to a limiting droplet diameterd_(T1), interplate spacing T2 is established to determine anotherlimiting droplet diameter d_(T2) in accordance with the relation (d_(T1)/d_(T2))² = T1/T2.
 3. The separator defined in claim 1 wherein theinterplate spacing T is 15 to 30 mm.
 4. The separator defined in claim 1wherein at least one of the plate members at each of said pockets isprovided with spacing formations engaging the other plate member at therespective pocket at the inlet to each pocket.
 5. The separator definedin claim 1 wherein said stack has an outlet region at which said gasstream emerges from said corrugations, the plates in said outlet regionbeing formed with undulations having a crest-to-crest spacing which issmaller than λ.